Developer material mixtures are known which consist of both toner particles and carrier particles. The toner particles are carried by the carrier particles to which they adhere due to electrostatic attraction forces. Upon being stewn upon an illuminated transfer surface the toner particles are picked up from a photoconductive layer of the transfer surface in order to develop the image. The toner particles are used up by this means and it becomes necessary to replenish them. Such replenishment is known and can be effected either by hand or automatically. The utilisation of the toner depends upon the number of copies to be developed, upon the particular size of the image surface, and upon the required blackness of the image. It is also known to monitor the originals being copied by optical means and to control the replenishment of the developer in dependence thereon.
One method, for example as described in German Patent Specification No. 1772295, uses a metering valve. In this known arrangement the metering valve is actuated in dependence upon the number of copies produced, and indeed according to a manual setting the valve is operated upon a predetermined cycle count in relation to the copy count.
It is also known from German published patent application No. 2141677 to provide a roller in the bottom opening of a supply reservoir, the roller being driven by drive means. This roller defines solely the opening formed in conformity therewith and throws toner into a developer supply reservoir positioned immediately beyond the edge of the opening towards which the roller advances in its direction of rotation. This results in a considerable spraying of the toner which in general adversely affects a thorough mixing of it.
This roller drive means, in one arrangement, comprises a manually adjustable electric current source which powers a driving motor for the roller, possibly intermittently at a constant speed of rotation.
The roller forming the closure member for the opening may have a profiled surface.
The drive, particularly the intermittent drive of the roller forming the closure member, is rendered problematical on account of the considerable contamination which is unavoidable in the neighbourhood of a powder scattering device. If a drive motor is used, it is also necessary to incorporate constructionally expensive coupling devices. Such coupling devices are impracticable however when there is more than a certain degree of contamination present. The same applies also for expensive engagement or meshing elements necessary for the creation of driving engagement between the parts.